A Microfluidic Device With Integrated Fluorimetric Detection For Flow Injection Analysis

This work describes the development of flow analysis microsystems with integrated fluorimetric detection cells. Channels (width of 300-540 μm and depth of 200-590 μm) were manufactured by deep-UV lithography in urethane-acrylate (UA) resin. Plastic optical fibers (diameter of 250 μm) were coupled to a 2.0-mm-long detection channel in order to guide the excitation radiation from an LED (470 nm) and collect the emitted radiation at a right angle towards a photomultiplier. A single-line miniaturized system, with a total internal volume of 10.4 μL, was evaluated by means of standard fluorescein solutions (0.53-2.66 μmol L-1, pH 8.5). The analytical signals presented a linear relationship in the concentration range studied, with a relative standard deviation of 1.9% (n=5), providing a detection limit of 0.37 μmol L-1 and an analytical frequency of 60 samples/h, using a flow rate of 60 μL min-1. Optical microscopy images and videos acquired in real time for the hydrodynamic injection of 130 and 320 nL of sample solutions indicated the good performance of the proposed sampling strategy. Another microsystem with a total internal volume of 38 μL was developed, incorporating a confluence point for two solutions. This device was applied to the determination of the total concentration of Ca2+ and Mg 2+ in commercial mineral waters using the calcein method. Microscopy images and videos demonstrated the mixing efficiency of the solutions in the microchannels. A linear relationship was observed for the analytical signal in the Ca2+ concentration range from 25 to 125 μmol L-1, with relative standard deviations of 3.5%. The analysis of mineral waters with the proposed system provided results that did not differ significantly from those obtained by the EDTA titration method at a confidence level of 95%. 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